Hydrogenation using palladium catalyst

Sato et al. carried out detailed studies on the possibilities of transformation of tetrazolo[l,5-tf]pyrazines 54 to 2-aminopyrazines 56 < 1994S931 >. These authors found that the generally used methods for this conversion fail because the starting compound exists in the stable bicyclic form 54, whereas partial formation of the azide valence bond isomer 55 would be necessary for the success of the transformation. Application of special reaction conditions succeeded, however hydrogenation over palladium catalyst in the presence of ammonium hydroxide or treatment with stannous chloride in a mixture of methanol and hydrochloric acid solved this problem. Thus, a great number of derivatives of 54 was reduced to the corresponding 2-aminopyrazine 56 in medium to high yields (45-100%). 

Reduction of furan and its homologs is readily achieved by catalytic hydrogenation using palladium [419, nickel [420] or Raney nickel [421 as catalysts. Too energetic conditions are to be avoided since hydrogenated furan rings are easily hydrogenolyzed [422,423. ... 

The reaction of ethyl 2-phenyl-4//-furo[3,2-/>]pyrrole-5-carboxylate (94) with 2-nitrobenzyl-oromide afforded ethyl 4-(2-nitrobenzyl)-2-phenylfuro[3,2-6]pyrrole-5-carboxylate (269) under conditions of phase transfer catalysis by utilization of sodium carbonate and tetrabutylammonium bromide. This product (269) was hydrogenated using palladium-on-charcoal catalyst to give the amine (270), which cyclized in the presence of 2-hydroxypyridine to give 2-phenylfuro[2, 3 4,5]pyrrolo[2,l-c]benzo[l,4]diazepin-l 1-one (271) <92CCC1487>. 

The oxidation on a laboratory scale can be carried out easily in a way similar to the hydrogenation of alkenes under atmospheric pressure of hydrogen using palladium black as a catalyst, tead of palladium black and hydrogen, the oxidation is carried out with PdCh and a copper salt under an oxygen atmosphere at room temperature using a similar tq>paratus. However, rates and yields of the oxidation are heavily dependent on the structure of alkenes. Also, the proper selection of solvents and reoxidants is crucial this is surveyed in the following sections. 

Hydrogenation is effected over Raney nickel at 100-130 atm. Low-pressure hydrogenation over palladium catalysts has also been used for the succinates. ... 

A much more frequently used reaction is the cleavage of unsaturated compounds to aldehydes (equations 98 and 99). Alkenes and cycloalkenes that possess one or two hydrogens at the double bonds are oxidized by ozone to ozonides, which have to be reduced to prevent a subsequent oxidation to acids by the excess oxygen atom. Reductions are carried out, usually without isolation of the ozonides, by catalytic hydrogenation over palladium catalyst [80, 81,1106] or Raney nickel [55] or by treatment with... 

Dehalogenation of 5,8-dichloropyrazino[2,3-with hydrogen using palladium on charcoal as catalyst and concentrated ammonium hydroxide at room temperature.86... 

Enantioselective hydrogenations using palladium on carbon as the catalyst in the presence of (,S )-proline have been reported40,41. This system is quite different from other heterogeneous enantioselective catalysts since the chiral agent is in solution together with the substrate, not merely on the surface of a previously prepared catalyst. This method has been effective in the hydrogenation of a./Tunsaturated ketones. A chiral iminium salt is considered as an intermediate, its C=N double bond is reduced with up to 60% optical purity. 

Padgett R.E. and Beamer R.L. (1964) Stereospecific hydrogenation using palladium-on-silica gel catalysts, J. Pharm. Sci. 53,689-690. 

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